Conventionally, photosensitive resin compositions which undergo changes in chemical structure by irradiation with active energy rays such as light, infrared rays, electron beams, or X-rays are used for various applications.
As such a photosensitive resin composition, a chemically amplified resist containing a photoacid generator which generates strong acid by irradiation with active energy rays is, for example, known. In this chemically amplified resist, the strong acid generated by irradiation with active energy rays acts on a resin component as a catalyst to change the solubility in a developer, thereby forming a pattern. Up to present, for the purpose of enhancing the sensitivity and the resolution, various resist materials have been developed, but the combination between the photoacid generator and the resin is limited, and development of a new chemically amplified resist is desired.
The light-curing techniques of monomers and prepolymers by irradiation with active energy rays are roughly classified into three types of the radical type, the cation type, and the anion type. Among these, a technique of polymerizing vinyl monomers by photoirradiation of a photo-radical initiator is most widely developed. Further, a technique of performing cationic polymerization by generating an acid using the action of light and using the acid as a catalyst has been studied.
However, in the case of such radical polymerization type, the polymerization reaction is inhibited by oxygen in air, and therefore a special devisal to block oxygen is necessary. Further, in the case of the cationic polymerization type, it is advantageous in that there is no inhibition by oxygen, but the corrosivity of the strong acid generated from the residual photoacid generator after curing and possible modification of the resin have been pointed out. Therefore, development of a photosensitive resin composition which is free from corrosive materials such as strong acid and allows a reaction to proceed rapidly with high efficiency without inhibition by oxygen in air has been strongly desired.
In such a situation, a photosensitive resin composition containing an anionic photobase generator using base generated by the action of light for polymerization reactions or chemical reactions has been proposed. However, as compared with radical photopolymerization initiators and cationic photoacid generators, anionic photobase generators have disadvantages of having poor photosensitivity and requiring irradiation with strong active energy.
Patent Literature 1 discloses a photosensitive resin composition containing a photobase generator configured to generate base by the action of light, an epoxy resin having a carboxyl group, and a curing agent having a thiol group. A basic amine compound is first generated by irradiating the aforementioned photosensitive resin with light, followed by heat treatment, thereby allowing a reaction of the generated amine compound with an epoxy group to obtain a cured film.
However, in such a photobase generator as used in Patent Literature 1, the amine generated by photoirradiation is monofunctional, and therefore a polyfunctional thiol monomer needs to be used in combination in order to obtain a cured film at a high residual film ratio. The polyfunctional primary thiol monomer is reactive with the epoxy resin even at room temperature, and thus the photosensitive resin composition has a short pot life, which has been a problem.
Further, the photobase generator used in Patent Literature 1 has a phenolic hydroxyl group in the molecule, and therefore the reaction of the epoxy group proceeds by heating also in the sites which are not subjected to photoirradiation. Therefore, in the case of using the photosensitive resin composition as a resist, a cured film is formed also in unexposed portions, and thus it has been difficult to faithfully reproduce a mask pattern.